The present invention relates to digital photography and particularly to taking wide-angle photographs, as well as transforming wide-angle photographs into digital panoramic images.
The present invention also relates to presenting digital panoramic images on a screen and virtual visits of places by means of panoramic images.
In recent years, the fast progress of micro-computing and manufacturing techniques of digital cameras have led to a substantial development in digital photography and the access thereto by the public.
Among the various applications offered by digital photography, the presentation of 360° panoramic images on computer screens has undergone a considerable boom as it is possible with this technique to produce virtual visits of places using a simple computer screen with a reduced viewing angle, the observer being able, by means of the screen pointer, to drag the image presented on the screen to the left, the right, upwards or downwards, up to the limits of the panoramic image. These panoramic images have generally a spherical or cylindrical appearance, such that the observer can at least go completely round the image in the horizontal plane and come back to the starting point. Furthermore, with spherical images it is possible to go completely around the image in the vertical plane. Moreover, by providing hyper-anchor type links between two panoramic images the observer can change from one image to another by a simple “click” on the mouse in an active zone present in the image. The active zone generally corresponds to an object present on the image, such as a door or a window for example.
Various examples of panoramic images and virtual visits are presented on many Web sites. In particular, reference is made to the site “http://www.panoguide.com” (“the guide to panoramas and panoramic photography”) that gives exhaustive insight into all the products available to the public, from photography equipment to software used to form 360° panoramic images by assembling wide-angle photographs, to correct the color of images, to produce active zones producing chains of panoramic images. These software programs, that implement mathematical algorithms for digital image processing, are offered to the public in the form of programs downloadable on the Internet or on CD-ROMs available in stores.
To date, despite increasing access to the public and the general craze for them, these techniques for obtaining digital panoramic images and virtual visits have several disadvantages that will be explained below.
Disadvantages of the Photography Equipment
It must be specified here that obtaining a 360° digital panoramic image generally requires taking at least two 180° photographs (or N photographs taken with an angle of 360°/N) by means of a panoramic lens and a pan head, as 360° lenses are expensive and have a small camera angle in the vertical plane. Such a pan head comprises one rotatably mounted part that receives the camera and that comprises means for adjusting the position of the camera, after several adjustments of which, the nodal plane of the lens can be aligned with the axis of rotation of the pan head, which is essential to avoid parallax errors. Yet, this alignment is not easy to obtain and requires several adjustments and tests. Furthermore, the pan heads are precision instruments that are quite considerable in price.
Furthermore, SLR (“Single Lens Reflex”) type digital cameras can receive any type of lens but they are expensive and not very accessible to the general public, which generally turns towards compact digital cameras, i.e. with a fixed lens. To overcome the disadvantage created by the irremovability of the lens of compact cameras, certain manufacturers offer lenses called adapters (“conversion lenses”) which include panoramic adapter lenses (“fisheye conversion lenses” or “fisheye converters”) and telephoto lens-type adapters (“tele-converter lenses”). These adapter lenses can be screwed directly onto the fixed lens of the compact camera, the back lens of the adapter lens thus being opposite the front lens of the fixed lens, and enable the owner of a compact camera to take wide-angle photographs. Unfortunately, these adapters are not universal and many compact cameras cannot receive them as they do not have the required thread.
Disadvantages of the Differences in Color between Panoramic Images
Another disadvantage of the above-mentioned techniques relates to the correction of the colors of the panoramic images obtained by assembling wide-angle photographs.
It must be specified here that after taking at least two digital wide-angle photographs, the photographic files delivered by the image sensor of the camera must be transferred into a microcomputer equipped with software executing image conversion algorithms. These algorithms transfer the image points of each photograph into a three-dimensional coordinate system, of the spherical, cubic, cylindrical, polyhedral type, etc. After the transfer, there are two semi-panoramic images, such as two images in hemispheres for example, that are assembled to obtain a total panoramic image, i.e., of 360°.
Disadvantages of the Orientation of Panoramic Images in a Virtual Visit
Another problem of the above-mentioned techniques, occurring in a virtual visit, is that the observer is subject to a phenomenon of disorientation during a transition from one panoramic image to the other, as he has no common point of reference between the different panoramas. This phenomenon is particularly noticeable in a virtual visit of a place comprising several adjoining rooms each represented by one or more panoramic images. For example, three adjoining rooms will be considered that each comprise a door to each of the other two rooms, and three panoramic images respectively representing each room and each comprising two active zones defined in the regions corresponding to the doors. The problem is to define the portion of panoramic image to be displayed on the screen when the observer enters a panoramic image.